1. Field of the Invention
The present invention relates to wireless communication systems. More specifically, but not exclusively, the present invention, relates to signal processors, communication units, a communication system and methods relating to transmission and reception of data streams in digital video broadcasting systems.
2. Description of the Related Art
A wireless broadcast system, such as a Digital Video Broadcasting (DVB) system, may transmit data in the form of a sequence of frames. A digital video broadcasting system may, for example, operate according to a Digital Video Broadcasting-Terrestrial version 2 (DVB-T2, Terrestrial 2nd Generation) standard, a Digital Video Broadcasting Next Generation Handheld (DVB-NGH) standard, or for example, according to the following families of standards: Advanced Televisions Systems Committee (ATSC), Integrated Services Digital Broadcasting (ISDB), or Digital multimedia Broadcasting (DMB). Each frame typically comprises a preamble section and a data section, the preamble section and the data section being time-multiplexed. The data section may carry data that is arranged in the form of a number of data streams that may be referred to as Physical Layer Pipes (PLP). A physical layer pipe may carry, for example, a service such as a video channel provided to a user. Reception of data from the frames, and reception of the data streams, may be assisted by signaling, which may typically be carried in the preamble of the frame, in which case the signaling may be referred to as Out-of-Band (OB) signaling and/or the signaling may be carried in the data section, typically of the preceding frame, in which case the signaling may be referred to as In-Band (IB) signaling. The signaling may be referred to as physical layer signaling, or Layer 1 (L1) signaling.
The preamble section of a frame may include various parts, including an L1-Config (configuration) part and an L1-Dyn (dynamic) part. The L1-config part typically carries information which is valid for each frame of the super-frame, and is typically the same for each frame of the super-frame. The L1-Dyn part carries information which may vary from one frame to the next.
With increasing use of signal compression techniques, and provision of lower data rate services that may be more robust in particular mobile environments, the number of PLPs carried by a sequence of frames is potentially large, for example in DVB-T2 up to 255 PLPs may be supported. As at least some of the information transmitted varies between the different PLPs, the signaling information transmitted in the preamble portion may represent a large overhead per frame in terms of data capacity. In particular, the L1-Config part typically takes up a high proportion (for example, more than 60%) of the signaling information of the preamble section. As a result, the overhead from the L1-Config is particularly high.
Digital video broadcasting systems supporting provision of multimedia content, such as DVB-T2, have in general the following resources: a Number (N) of Radio Frequencies (RFs) (where N≧1), each with a given Bandwidth (B); and where the signal on each RF frequency occupies a given time Duration (D).
FIG. 1 illustrates a generic frame structure for provision of transport streams of data according to the related art.
FIG. 1 illustrates a generic frame structure 100 for provision of transport streams of data. The data services 102, 104 are generally arranged in transport streams, e.g., stream of data packets 106, for delivery over a target digital video broadcasting system. One goal in designing a multimedia data structure such as in DVB-NGH is to organize efficiently and flexibly the delivery of the transport streams within the physical resources of the digital video broadcasting system.
Each transmitted frame (and therefore the subsequently received frame) 118 typically comprises a preamble section 112 and a data section 114, wherein the preamble section 112 and the data section 114 are time-multiplexed. The transmitted received frames 118 are sent on two radio frequencies, RF1 108, RF2 110 in this simple illustration. The data section 114 may carry data that is arranged in the form of a number of data streams that may be referred to as PLPs. A PLP may carry, for example, a service such as a video channel provided to a user. Reception of data decoded from the received frames may be assisted by use of signaling fields/data/bits, etc., which may typically be carried in the preamble section 112 of the frame. The signaling is often referred to as physical layer signaling, or L1 signaling. The signaling may indicate a modulation or coding scheme to be used for decoding data, and it may for example indicate sections of a data field to be decoded, or the location of a data stream within the data section.
Digital Video Broadcasting frame structures may provide physical slots within the DVB physical frame structure, which are reserved in a standard for future use, for example referred to as Future Extension Frame (s) slots 116, which are time multiplexed with a given DVB-T2 signal. For example, Future Extension Frame slots 116 may be provided for transmission of signals intended for reception by mobile Digital Video Broadcasting receivers in addition to transmission of signals intended for reception by conventional fixed Digital Video Broadcasting receivers.
Digital video broadcasting systems may provide for the transmission of signals specifically intended for reception by hand held devices, as such as NGH receivers. Such signals may be, for example, of lower bandwidth and have more robust modulation and coding than signals intended for reception by fixed receivers.
There have been recent proposals to use the additional physical slots in DVB-T2, such as the FEF slots, for the transmission of DVB-NGH signals intended for reception by handheld receivers. Typically, a frame for the transmission of a signal intended for reception by a handheld receiver would be transmitted within the additional physical slot of a sequence of frames for the transmission of a signal intended for fixed receivers, including signaling information for the frame, which would be typically transmitted as a preamble in each FEF slot 116.
However, such a scheme will suffer from a limited capacity, due to the short physical slot duration and relatively high signaling overhead. Furthermore, such a scheme will be limited in terms of achievable statistical multiplexing gain, due to the limited capacity that may be achieved as a consequence of the relatively few PLPs being available for use.
Thus, a need exists for signal processors, communication units, a wireless system and methods relating to transmission and reception of data streams in digital video broadcasting systems that may address one or more deficiencies in the known art.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.